The online creator's 7-Zip self extracted files have started to get broken as soon as they're modified with 7-Zip.Why modify? Because, for example, I want to replace the encryption plugin with SecureVNCPlugin.By broken I mean you can't run them. Any attempt to do so displays a "7-Zip - Unsupported Method" message followed by "Z-Zip - Unspecified error".

I've approached 7-Zip's creator with this bug, but he turned it back to you:

Probably they use some old 7-Zip code without LZMA2 support.So ask them to upgade sfx code to new 7-Zip code with LZMA support.

So can you please do so?

What he means is that you use LZMA, so when 7-Zip modifies the files it uses LZMA2 despite you only supporting LZMA.